• Journal of Applied Reliability
• /
• v.17 no.4
• /
• pp.325-331
• /
• 2017

Purpose: There is active research that improves both reliability and fatigue life of structures which widely used in the aerospace fields of defense industry. The effects of three parameters (pressure, peening time, nozzle distance) on Almen intensity and coverage will be investigated by using the experimental and analyzed data. Methods: we employed a Box-Behnken design. Additionally, to verify the validity of the optimal condition obtained from experimental results, metallurgical analyses of the shot-peened aerospace part were conducted with respect to surface morphology, residual stress. Results: Optimal shot peening condition is determined as (distance, pressure, time) by optimizing simultaneously the two responses of intensity and coverage. At the optimal peening condition the prediction interval for Almen intensity is well within the required range. And, the validity of the condition was checked by using the real aerospace aluminum alloy plate. Conclusion: Shot peening introduces significant levels of compressive residual stress and induces improves both reliability and fatigue life of structures.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.5
• /
• pp.89-94
• /
• 2003

Rolling stock structures such as bogie frame and car body play an important role for the support of vehicle leading. In general, more than 25 years' durability is needed for them. A lot of study has been carried out for the prediction of the fatigue life of the bogie frame and car body in experimental and theoretical domains. One of the new methods is a probabilistic fatigue lift evaluation. The objective of this paper is to estimate the fatigue lift of the bogie frame of an electric car, which was developed by the Korea Railroad Research Institute (KRRI). We used two approaches. In the first approach probabilistic distribution of S-N curve and limit state function of the equivalent stress of the measured stress spectra are used. In the second approach, limit state function is also used. And load spectra measured by strain gauges are approximated by the two-parameter Weibull distribution. Other probabilistic variables are represented by log-normal and normal distributions. Finally, reliability index and structural integrity of the bogie frame are estimated.

• Journal of the Society of Naval Architects of Korea
• /
• v.28 no.2
• /
• pp.228-240
• /
• 1991

Many experimental data of fatigue crack propagation show that the fatigue crack propagation process is stochastic. Therefore, the study on the crack propagation must be based on the probabilistic approach. In the present paper, fatigue crack propagation process is assumed to be a discrete Markov process and the method is developed, which can evaluate the reliability of the structural component by using Markov chain model(Unit step B-model) suggested by Bogdanoff. In this method, leak failure, plastic collapse and brittle fracture of the critical component are taken as failure modes, and the effects of initial crack distribution, periodic and non-periodic inspection on the probability of failure are considered. In this method, an equivalent load value for random loading such as wave load is used to facilitate the analysis. Finally some calculations are carried out in order to show the usefulness and the applicability of this method. And then some remarks on this method are mentioned.

• 한국방재학회:학술대회논문집
• /
• 2007.02a
• /
• pp.67-70
• /
• 2007

A methodology to evaluate fatigue vulnerability of steel bridge members affected by corrosion and truck traffic variation is proposed. A fatigue limit state function including corrosion and traffic variation effects is established to make the criterion whether the steel bridge member is damaged by fatigue. Corrosion effects are expressed as increase of the average corrosion depth, and the traffic variation effects are modeled as the accumulated number of stress cycles. Reliability analysis is carried out by Monte-Carlo simulation method for the fatigue limit state function. The methodology Proposed is verified by comparing reference study and applying for the steel bridge in service.

• International Journal of Highway Engineering
• /
• v.18 no.4
• /
• pp.63-68
• /
• 2016

PURPOSES : The nonlinear model of fatigue cracking is typically used for determining the maintenance period. However, this requires that the model parameters be known. In this study, the particle filter (PF) method was used to determine various statistical parameters such as the mean and standard deviation values for the nonlinear model of fatigue cracking. METHODS : The PF method was used to determine various statistical parameters for the nonlinear model of fatigue cracking, such as the mean and standard deviation. RESULTS : On comparing the values obtained using the PF method and the least square (LS) method, it was found that PF method was suitable for determining the statistical parameters to be used in the nonlinear model of fatigue cracking. CONCLUSIONS : The values obtained using the PF method were as accurate as those obtained using the LS method. Furthermore, reliability design can be applied because the statistical parameters of mean and standard deviation can be obtained through the PF method.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.2
• /
• pp.473-480
• /
• 1996

Automatic fatigue crack length measuring system using DC electrical potential method and the system control program for automatic fatigue testing under random load condition were made in this study. And using these system and control program, fatigue tests were executed under constant and random load condition. As the result, the propagation of crack in random loading can be represented Paris equaiton and log normal probability function. But constant and random load test show different crack propagation properties.

• Journal of the Korean Ceramic Society
• /
• v.33 no.3
• /
• pp.321-326
• /
• 1996

Thermal fatigue test and stress analysis of Si3N4 and metal swirl chamber were carried out to investigate the reliability of the swirl chambers. Conditions of the thermal fatigue test were severer than those in real engine and FEM was used to analize the stress distribution in the swirl chambers. Fatigue cracks of the maximum length 2.4 mm and deformation were occurred at the corner of the jet in metal swirl chamber but not observed in Si3N4 swirl chamber. Maximum tensile stress in Si3N4 swirl chamber calculated by FEM was 300 MPa.

• Journal of Welding and Joining
• /
• v.26 no.4
• /
• pp.55-60
• /
• 2008

Structural reliability of electrical panels installed in naval vessels is of critical importance from structural performance viewpoint. The panels may be exposed to vibration and fatigue loadings from internal and external sources and wave loading which cause fatigue cracking. In this study, common methods such as burr grinding and post weld heat treatment (PWHT), for the fatigue strength improvement of weldments are investigated. Burr grinding is carried out using a electric grinder in order to remove surface defects and improve the weld bead profile. And also PWHT is carried out for the purpose of removing residual. The effectiveness of the two post treatment methods is evaluated in terms of fatigue strength improvement of welded structures.

• Transactions of Materials Processing
• /
• v.19 no.2
• /
• pp.88-94
• /
• 2010

The next generation of diesel engine can operate at high injection pressure up to 1,800bar. The common rail pipe must have higher internal strength because it is directly influenced by the high-pressure fuel. Folding defects in the Common rail pipe can not ensure the structural safety. Therefore, Preform design and fatigue-life analysis are very important for preventing the head of the common rail pipe from folding in the heading process and for predicting fatigue life according to the amount of folding. In this study, a closed form equation to predict fatigue life was suggested by Goodman theory and pressure vessels theory in ASME Code in order to develop an optimization technique of the heading process and verified its reliability through fatigue-structural coupled field analysis. The results calculated by the theory were in good agreement with those obtained by the finite element analysis.

• Journal of the Microelectronics and Packaging Society
• /
• v.30 no.4
• /
• pp.105-111
• /
• 2023

Electronic devices have been evolved to be mechanically flexible that can be endured repetitive deformation. This evolution emphasizes the importance of long-term reliability in metal wiring connecting electronic components, especially under bending fatigue in compressed environments. This study investigated methods to enhance adhesion between copper (Cu) and polyimide (PI) substrates, aiming to improve the reliability of copper wiring under such conditions. We applied oxygen plasma treatment and introduced a chromium (Cr) adhesion layer to the polyimide substrate. Our findings revealed that these adhesion enhancement methods significantly affect compression fatigue behavior. Notably, the chromium adhesion layer, while showing weaker fatigue characteristics at 1.5% strain, demonstrated superior performance at 2.0% strain with no delamination, outperforming other methods. These results offer valuable insights for improving the reliability of flexible electronic devices, including reducing crack occurrence and enhancing fatigue resistance in their typical usage environments.